Electrons' roundness frustrates researchers

Experiment finds no signs of asymmetry, which would point to undiscovered particles

Electrons are incredibly spherical, an experiment reveals, throwing into doubt popular theories that would add new species to the universe’s particle zoo.

Physicists determine the shape of electrons by measuring their distribution of charge, known as an electric dipole moment, or EDM. A perfectly spherical electron’s EDM would be zero. But according to quantum mechanics, other charged particles constantly popping in and out of existence exert subtle tugs that should deform electrons and create a slight EDM (SN: 2/12/11, p. 22).

Yale physicist David DeMille and colleagues tried to get electrons to flop over by exposing them to an electric field, much like eggs set on end topple over due to gravity. Electrons would tumble only if they had a nonzero EDM. When researchers confined electrons within thorium monoxide molecules and cranked up the field strength, the electrons didn’t budge. The result, published December 19 in Science, shows that despite a measurement with about 10 times the sensitivity of previous ones, the electron appears perfectly spherical.

The finding rules out some theories of supersymmetry, which predict the existence of novel particles that would stretch electrons to a degree detectable by the new experiment.